To facilitate discussion FIG. 1 is a schematic view of a single stage optical network 100 that may be used in the prior art. The optical network 100 may comprise a 256×256 active optical switch 108 and a 256×256 protection optical switch 112. The protection optical switch 112 acts as a backup for the active optical switch 108. A plurality of 1×2 input switches 116, 118, 120 have outputs connected to the input sides of the active optical switch 108 and the protection optical switch 112. A first ingress fiber 124 provides input to the first 1×2 input switch 116. A second ingress fiber 126 provides input to the second input switch 118. An nth ingress fiber 128 provides input to the nth input switch 120. A plurality of 2×1 output switches 136, 138, 140 have inputs connected to the output sides of the active optical switch 108 and the protection optical switch 112. A first egress fiber 144 receives output from the first 2×1 output switch 136. A second egress fiber 146 receives output from the second output switch 138. An nth ingress fiber 148 receives output from the nth output switch 140. In this example, n may be 256 for a 256×256 optical switch.
In operation, the active optical switch 108 is normally used to provide switching, while the protection optical switch 112 may be used as a backup, if the active optical switch 108 malfunctions. During such an operation, a first signal from a user may be placed through the first ingress fiber 124 to the first input switch 116. During normal operation, the first input switch 116 directs the first signal to the active optical switch 108, which directs the signal to one of the output switches 136, 138, 140, which for example may be the first output switch 136. The first output switch 136 directs the first signal to the first egress fiber 144. Similarly, a second signal may pass from the second ingress fiber 126 through the second input switch 118 to the active optical switch 108. The active optical switch 108 may, for example, pass the second signal to the nth output switch 140, which passes the signal to the nth egress fiber 148. Similarly, a third signal may pass from the third ingress fiber 128 through the third input switch 120 to the active optical switch 108. The active optical switch 108 may, for example, pass the third signal to the second output switch 138, which passes the signal to the second egress fiber 146. If a malfunction is detected in the having all of the input switches 116, 118, 120 direct input to the protection optical switch 112 and having all of the output switches 136, 138, 140 receive signals from the protection optical switch.
It is desirable to provide a system that determines whether the protection optical switch or other switches not in current use are properly working.